A DIMM, or dual in-line memory module, comprises a series of dynamic random access memory integrated circuits. These modules are mounted on a printed circuit board and are designed for use in personal computers, workstations and servers. Some memory technologies use DIMMs in conjunction with flash memory chips. DIMMs can be formed to contain hundreds of flash memory chips. The manufacturing process that is used to produce these products can involve operations that include heating and attaching the flash memory chips to the DIMMs.
During the manufacturing process, for various reasons, the threshold voltages of individual memory cells of a memory device can shift relative to a static reference. When this occurs, the memory cells whose threshold voltages have shifted can be rendered unreadable. This can be especially problematic at power-up before the chip has loaded “tuning” information.
Approaches used to address the problem of threshold voltage shifts include using dynamic reference cells to track shifts in the threshold voltage of core memory cells and erasing and reprogramming parts. Dynamic reference cells attempt to track shifts in core memory cell threshold voltage such that data stored in the core memory cells can be read correctly. However, a significant shortcoming of this approach is that the dynamic reference cells themselves are susceptible to threshold voltage shifts and are not particularly effective with regard to threshold voltage shifts of core memory cells that are not small. In practice the voltage shifts exhibited by the dynamic reference cells themselves can be so large that the dynamic reference cells simply can not keep track of the threshold voltage shifts of the core memory cells.
Erasing and reprogramming parts attempts to address the problem of threshold voltage shifts of memory cells by erasing and reprogramming the memory cells in order to cause the memory cells to read correctly. However, erasing and reprogramming parts is practical for only a small number of applications and can involve loading software from an external device which exacts a significant time cost. Consequently, conventional approaches have proven to be unsatisfactory as it relates to addressing threshold voltage shifts of memory cells in electronic products.